Fuel tank depressurization before refueling a plug-in hybrid vehicle

ABSTRACT

A method for operating a vehicle system is provided. The method includes monitoring a change in a temperature of the fuel vapor canister coupled to a fuel tank via a canister temperature sensor and adjusting operation of a fuel tank isolation valve based on the change in temperature of the fuel vapor canister.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation-in-part of U.S. patent application Ser. No. 13/906,187, entitled “FUEL TANK DEPRESSURIZATION BEFORE REFUELING A PLUG-IN HYBRID VEHICLE,” filed May 30, 2013, the entire contents of which are hereby incorporated by reference for all purposes.

FIELD

The field of the present disclosure relates to motor vehicle fuel systems.

BACKGROUND/SUMMARY

It may be desirable to vent fuel tanks to reduce pressure therein to reduce the likelihood of overpressure conditions in the fuel tank. Venting the fuel tank may include flowing air/vapors to a fuel vapor canister and/or venting fuel vapors via a fuel cap. In the case of plug in hybrid vehicles, the internal combustion engine may not operate for a prolonged period of time. In such systems, the fuel tank are sealed and can reach high pressures, necessitating additional venting operation and further exacerbating the aforementioned problem of fuel tank over-pressurization. Fuel tank sensors may be used as an indicator for venting operation. Venting operation may rely upon pressure sensors positioned in the fuel tank. The pressure sensors in the vehicle's fuel tank can fail, leading to problems such as fuel tank over-pressurization and subsequent fuel tank degradation and in some case failure.

The inventors herein have recognized an issue with the above type of systems and developed a method for operating a vehicle system. The method includes monitoring a change in a temperature of the fuel vapor canister coupled to a fuel tank via a canister temperature sensor and adjusting operation of a fuel tank isolation valve based on the change in temperature of the fuel vapor canister. It will be appreciated that the change in temperature of the fuel vapor canister can be correlated to a fuel tank pressure. This correlation can be useful when a fuel tank pressure sensor is degraded. Therefore, the aforementioned method may be implemented subsequent to fuel tank pressure sensor degradation, in one example. Consequently, venting operation, implemented via opening and closing of the fuel tank isolation valve, can rely upon multiple sensors (i.e., a fuel tank pressure sensor as well as a fuel vapor canister temperature sensor), increasing the reliability of and improving venting operation in the vehicle system. In another example, the monitored change in temperature of the fuel vapor canister can be used to determine fuel tank pressure sensor functionality. In this way, the temperature sensor can also be used to improve fuel tank pressure sensor diagnostics.

The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.

It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows an example vehicle propulsion system.

FIG. 2 shows an example vehicle system with a fuel system.

FIG. 3 shows an example method for unlocking a fuel cap in accordance with the disclosure.

FIG. 4 illustrates an example method for unlocking a fuel cap in accordance with the disclosure.

FIG. 5 shows an example method for operating a vehicle system.

FIG. 6 shows another example method for operating a vehicle system.

FIG. 7 shows another example method for operating a vehicle system.

FIG. 8 shows a graph depicting the correlation between a fuel vapor canister temperature, a fuel tank pressure, and a duty cycle of the fuel tank isolation valve.

DETAILED DESCRIPTION

The following description relates to systems and methods for operating a vehicle system based on a change in temperature of a fuel vapor canister. The vehicle includes an engine system with a fuel system, as shown in FIG. 2, where the fuel system includes a fuel tank and a fuel cap with a locking mechanism configured to prevent the fuel cap from being opened. The fuel tank may be depressurized in order prevent fuel discharging from a fuel filler pipe during refueling. As such, the fuel cap may remain locked until the fuel tank is sufficiently depressurized. As described below with reference to FIGS. 3 and 4, following a refueling request the fuel tank may be vented to a fuel vapor canister and the temperature in the fuel vapor canister may be monitored to assist in determining when the fuel tank is sufficiently depressurized so that refueling may be performed. For example, a predetermined temperature change in the fuel vapor canister may be used to detect when the fuel tank has depressurized. In some examples, such detection may occur in the absence of a fuel tank pressure sensor, or when a fuel tank pressure sensor has degraded. In another aspect of the solution, the detection may also occur alternatively, or in addition to the features noted above, in response to both a pressure sensor and detection of a predetermined temperature change in the canister. Further in some examples, the pressure in the fuel tank may be inferred from the temperature of the fuel vapor canister and a fuel tank isolation valve may be adjusted based on the fuel tank pressure inference. In this way, the fuel tank pressure can be inferred to improve fuel tank isolation valve operation in the case of fuel tank pressure sensor degradation or failure.

Turning now to the figures, FIG. 1 illustrates an example vehicle propulsion system 100. Vehicle propulsion system 100 includes a fuel burning engine 110 and a motor 120. As a non-limiting example, engine 110 comprises an internal combustion engine and motor 120 comprises an electric motor. Motor 120 may be configured to utilize or consume a different energy source than engine 110. For example, engine 110 may consume a liquid fuel (e.g., gasoline) to produce an engine output while motor 120 may consume electrical energy to produce a motor output. As such, a vehicle with propulsion system 100 may be referred to as a hybrid electric vehicle (HEV).

Vehicle propulsion system 100 may utilize a variety of different operational modes depending on operating conditions encountered by the vehicle propulsion system. Some of these modes may enable engine 110 to be maintained in an off state (i.e. set to a deactivated state) where combustion of fuel at the engine is discontinued. For example, under select operating conditions, motor 120 may propel the vehicle via drive wheel 130 as indicated by arrow 122 while engine 110 is deactivated.

During other operating conditions, engine 110 may be set to a deactivated state (as described above) while motor 120 may be operated to charge energy storage device 150. For example, motor 120 may receive wheel torque from drive wheel 130 as indicated by arrow 122 where the motor may convert the kinetic energy of the vehicle to electrical energy for storage at energy storage device 150 as indicated by arrow 124. This operation may be referred to as regenerative braking of the vehicle. Thus, motor 120 can provide a generator function in some embodiments. However, in other embodiments, generator 160 may instead receive wheel torque from drive wheel 130, where the generator may convert the kinetic energy of the vehicle to electrical energy for storage at energy storage device 150 as indicated by arrow 162.

During still other operating conditions, engine 110 may be operated by combusting fuel received from fuel system 140 as indicated by arrow 142. For example, engine 110 may be operated to propel the vehicle via drive wheel 130 as indicated by arrow 112 while motor 120 is deactivated. During other operating conditions, both engine 110 and motor 120 may each be operated to propel the vehicle via drive wheel 130 as indicated by arrows 112 and 122, respectively. A configuration where both the engine and the motor may selectively propel the vehicle may be referred to as a parallel type vehicle propulsion system. Note that in some embodiments, motor 120 may propel the vehicle via a first set of drive wheels and engine 110 may propel the vehicle via a second set of drive wheels.

In other embodiments, vehicle propulsion system 100 may be configured as a series type vehicle propulsion system, whereby the engine does not directly propel the drive wheels. Rather, engine 110 may be operated to power motor 120, which may in turn propel the vehicle via drive wheel 130 as indicated by arrow 122. For example, during select operating conditions, engine 110 may drive generator 160, which may in turn supply electrical energy to one or more of motor 120 as indicated by arrow 114 or energy storage device 150 as indicated by arrow 162. As another example, engine 110 may be operated to drive motor 120 which may in turn provide a generator function to convert the engine output to electrical energy, where the electrical energy may be stored at energy storage device 150 for later use by the motor.

Fuel system 140 may include one or more fuel storage tanks 144 for storing fuel on-board the vehicle. For example, fuel tank 144 may store one or more liquid fuels, including but not limited to: gasoline, diesel, and alcohol fuels. In some examples, the fuel may be stored on-board the vehicle as a blend of two or more different fuels. For example, fuel tank 144 may be configured to store a blend of gasoline and ethanol (e.g., E10, E85, etc.) or a blend of gasoline and methanol (e.g., M10, M85, etc.), whereby these fuels or fuel blends may be delivered to engine 110 as indicated by arrow 142. Still other suitable fuels or fuel blends may be supplied to engine 110, where they may be combusted at the engine to produce an engine output. The engine output may be utilized to propel the vehicle as indicated by arrow 112 or to recharge energy storage device 150 via motor 120 or generator 160.

In some embodiments, energy storage device 150 may be configured to store electrical energy that may be supplied to other electrical loads residing on-board the vehicle (other than the motor), including cabin heating and air conditioning, engine starting, headlights, cabin audio and video systems, etc. As a non-limiting example, energy storage device 150 may include one or more batteries and/or capacitors.

Control system 190 may communicate with one or more of engine 110, motor 120, fuel system 140, energy storage device 150, and generator 160. As will be described by the process flow of FIG. 3, control system 190 may receive sensory feedback information from one or more of engine 110, motor 120, fuel system 140, energy storage device 150, and generator 160. Further, control system 190 may send control signals to one or more of engine 110, motor 120, fuel system 140, energy storage device 150, and generator 160 responsive to this sensory feedback. Control system 190 may receive an indication of an operator requested output of the vehicle propulsion system from a vehicle operator 102. For example, control system 190 may receive sensory feedback from pedal position sensor 194 which communicates with pedal 192. Pedal 192 may refer schematically to a brake pedal and/or an accelerator pedal. In one example, the control system 190 may be referred to as a control sub-system when it is incorporated into another vehicle system, such as the vehicle system 206, shown in FIG. 2 and discussed in greater detail herein.

Energy storage device 150 may periodically receive electrical energy from a power source 180 residing external to the vehicle (e.g., not part of the vehicle) as indicated by arrow 184. As a non-limiting example, vehicle propulsion system 100 may be configured as a plug-in hybrid electric vehicle (HEV), whereby electrical energy may be supplied to energy storage device 150 from power source 180 via an electrical energy transmission cable 182. During a recharging operation of energy storage device 150 from power source 180, electrical transmission cable 182 may electrically couple energy storage device 150 and power source 180. While the vehicle propulsion system is operated to propel the vehicle, electrical transmission cable 182 may disconnected between power source 180 and energy storage device 150. Control system 190 may identify and/or control the amount of electrical energy stored at the energy storage device, which may be referred to as the state of charge (SOC).

In other embodiments, electrical transmission cable 182 may be omitted, where electrical energy may be received wirelessly at energy storage device 150 from power source 180. For example, energy storage device 150 may receive electrical energy from power source 180 via one or more of electromagnetic induction, radio waves, and electromagnetic resonance. As such, it should be appreciated that any suitable approach may be used for recharging energy storage device 150 from a power source that does not comprise part of the vehicle. In this way, motor 120 may propel the vehicle by utilizing an energy source other than the fuel utilized by engine 110.

Fuel system 140 may periodically receive fuel from a fuel source residing external to the vehicle. As a non-limiting example, vehicle propulsion system 100 may be refueled by receiving fuel via a fuel dispensing device 170 as indicated by arrow 172. In some embodiments, fuel tank 144 may be configured to store the fuel received from fuel dispensing device 170 until it is supplied to engine 110 for combustion. In some embodiments, control system 190 may receive an indication of the level of fuel stored at fuel tank 144 via a fuel level sensor. The level of fuel stored at fuel tank 144 (e.g., as identified by the fuel level sensor) may be communicated to the vehicle operator, for example, via a fuel gauge or indication in a vehicle instrument panel 196.

The vehicle propulsion system 100 may also include an ambient temperature/humidity sensor 198, and a roll stability control sensor, such as a lateral and/or longitudinal and/or yaw rate sensor(s) 199. The vehicle instrument panel 196 may include indicator light(s) and/or a text-based display in which messages are displayed to an operator. The vehicle instrument panel 196 may also include various input portions for receiving an operator input, such as buttons, touch screens, voice input/recognition, etc. For example, the vehicle instrument panel 196 may include a refueling button 197 which may be manually actuated or pressed by a vehicle operator to initiate refueling. For example, as described in more detail below, in response to the vehicle operator actuating refueling button 197, a fuel tank in the vehicle may be depressurized so that refueling may be performed.

In an alternative embodiment, the vehicle instrument panel 196 may communicate audio messages to the operator without display. Further, the sensor(s) 199 may include a vertical accelerometer to indicate road roughness. These devices may be connected to control system 190. In one example, the control system may adjust engine output and/or the wheel brakes to increase vehicle stability in response to sensor(s) 199.

FIG. 2 shows a schematic depiction of a vehicle system 206. The vehicle system 206 includes an engine system 208 coupled to an emissions control system 251 and a fuel system 218. Emission control system 251 includes a fuel vapor container or canister 222 which may be used to capture and store fuel vapors. In some examples, vehicle system 206 may be a hybrid electric vehicle system.

The engine system 208 may include an engine 210 having a plurality of cylinders 230. The engine 210 includes an engine intake 223 and an engine exhaust 225. The engine intake 223 includes a throttle 262 fluidly coupled to the engine intake manifold 244 via an intake passage 242. The engine exhaust 225 includes an exhaust manifold 248 leading to an exhaust passage 235 that routes exhaust gas to the atmosphere. The engine exhaust 225 may include one or more emission control devices 270, which may be mounted in a close-coupled position in the exhaust. One or more emission control devices may include a three-way catalyst, lean NOx trap, diesel particulate filter, oxidation catalyst, etc. It will be appreciated that other components may be included in the engine such as a variety of valves and sensors.

Fuel system 218 may include a fuel tank 220 coupled to a fuel pump system 221. The fuel pump system 221 may include one or more pumps for pressurizing fuel delivered to the injectors of engine 210, such as the example injector 266 shown. While only a single injector 266 is shown, additional injectors are provided for each cylinder. It will be appreciated that fuel system 218 may be a return-less fuel system, a return fuel system, or various other types of fuel system.

Vapors generated in fuel system 218 may be routed to an evaporative emissions control system 251 which includes a fuel vapor canister 222 via vapor recovery line 231, before being purged to the engine intake 223. Fuel vapor canister 222 may include a buffer or load port 241 to which fuel vapor recovery line 231 is coupled. Further, a temperature sensor 243 (e.g., canister temperature sensor) may be included in fuel vapor canister 222 so that temperature changes in the fuel vapor canister may be monitored to assist in determining when the fuel tank is depressurized prior to refueling. The temperature sensor 243 may be located in load port 241 of fuel vapor canister 222 or in any other suitable location in canister 222. Fuel vapors undergo an exothermic reaction when carbon in the canister adsorbs vapor from the fuel tank thus the temperature of the fuel vapor canister, e.g., as determined by temperature sensor 243, may increase when the fuel tank is vented to the canister. Thus, as described below, temperature changes in the canister while the fuel tank is vented thereto may be used to determine an amount of pressure in the fuel tank. Further, temperature in the fuel vapor canister may decrease when pressure in the fuel tank is below atmospheric pressure, e.g., during vacuum conditions, since in this example, the vacuum in the fuel tank draws fuel vapor from the fuel vapor canister into the tank. This decrease in temperature in the canister while the fuel tank is vented to the canister may be used to determine when an amount of vacuum in the fuel tank falls below a threshold vacuum. In one example, the canister temperature sensor 243 may include one or more thermocouples. However, other types of temperature sensors have been contemplated.

Vapor recovery line 231 may be coupled to fuel tank 220 via one or more conduits and may include one or more valves for isolating the fuel tank during certain conditions. For example, vapor recovery line 231 may be coupled to fuel tank 220 via one or more or a combination of conduits 271, 273, and 275. Further, in some examples, one or more fuel tank isolation valves may be included in recovery line 231 or in conduits 271, 273, or 275. Among other functions, fuel tank isolation valves may allow a fuel vapor canister of the emissions control system to be maintained at a low pressure or vacuum without increasing the fuel evaporation rate from the tank (which would otherwise occur if the fuel tank pressure were lowered). For example, conduit 271 may include a grade vent valve (GVV) 287, conduit 273 may include a fill limit venting valve (FLVV) 285, and conduit 275 may include a grade vent valve (GVV) 283, and/or conduit 231 may include an isolation valve 253. Further, in some examples, recovery line 231 may be coupled to a fuel filler system 219. In some examples, fuel filler system may include a fuel cap 205 for sealing off the fuel filler system from the atmosphere. Refueling system 219 is coupled to fuel tank 220 via a fuel filler pipe or neck 211. Further, a fuel cap locking mechanism 245 may be coupled to fuel cap 205. The fuel cap locking mechanism may be configured to automatically lock the fuel cap in a closed position so that the fuel cap cannot be opened. For example, as described in more detail below, the fuel cap 205 may remain locked via locking mechanism 245 while pressure or vacuum in the fuel tank is greater than a threshold. In response to a refuel request, e.g., a vehicle operator initiated request, the fuel tank may be depressurized and the fuel cap unlocked after the pressure or vacuum in the fuel tank falls below a threshold.

A fuel tank pressure transducer (FTPT) 291, or fuel tank pressure sensor, may be included between the fuel tank 220 and fuel vapor canister 222, to provide an estimate of a fuel tank pressure. As described below, in some examples, during engine off conditions sensor 291 may be used to monitor changes in pressure and/or vacuum in the fuel system to determine if a leak is present. The fuel tank pressure transducer may alternately be located in vapor recovery line 231, purge line 228, vent line 227, or other location within emission control system 251 without affecting its engine-off leak detection ability. As another example, one or more fuel tank pressure sensors may be located within fuel tank 220.

Emissions control system 251 may include one or more emissions control devices, such as one or more fuel vapor canisters 222 filled with an appropriate adsorbent, the canisters are configured to temporarily trap fuel vapors (including vaporized hydrocarbons) during fuel tank refilling operations and “running loss” (that is, fuel vaporized during vehicle operation). In one example, the adsorbent used is activated charcoal. Emissions control system 251 may further include a canister ventilation path or vent line 227 which may route gases out of the canister 222 to the atmosphere when storing, or trapping, fuel vapors from fuel system 218.

Vent line 227 may also allow fresh air to be drawn into canister 222 when purging stored fuel vapors from fuel system 218 to engine intake 223 via purge line 228 and purge valve 261. For example, purge valve 261 may be normally closed but may be opened during certain conditions so that vacuum from engine intake 244 is provided to the fuel vapor canister for purging. In some examples, vent line 227 may include an air filter 259 disposed therein upstream of a canister 222.

Flow of air and vapors between canister 222 and the atmosphere may be regulated by a canister vent valve 229. Canister vent valve may be a normally open valve so that fuel tank isolation valve 253 may be used to control venting of fuel tank 220 with the atmosphere. For example, in hybrid vehicle applications, isolation valve 253 may be a normally closed valve so that by opening isolation valve 253, fuel tank 220 may be vented to the atmosphere and by closing isolation valve 253, fuel tank 220 may be sealed from the atmosphere. In some examples, isolation valve 253 may be actuated by a solenoid so that, in response to a current supplied to the solenoid, the valve will open. For example, in hybrid vehicle applications, the fuel tank 220 may be sealed off from the atmosphere in order to contain diurnal vapors inside the tank since the engine run time is not guaranteed. Thus, for example, isolation valve 253 may be a normally closed valve which is opened in response to certain conditions. For example, isolation valve 253 may be commanded open following a refueling request in so that the fuel tank is depressurized prior to refueling, as described below.

The vehicle system 206 may further include a control sub-system 214. Control system 214 is shown receiving information from a plurality of sensors 216 (various examples of which are described herein) and sending control signals to a plurality of actuators 281 (various examples of which are described herein). As one example, sensors 216 may include exhaust gas sensor 237 located upstream of the emission control device, temperature sensor 233, pressure sensor 291, and canister temperature sensor 243. Other sensors such as pressure, temperature, air/fuel ratio, and composition sensors may be coupled to various locations in the vehicle system 206. As another example, the actuators may include fuel injector 266, throttle 262, fuel tank isolation valve 253, pump 292, purge valve 261, canister vent valve 229, fuel pump system 226, and fuel cap locking mechanism 245. The control system 214 may include a controller 212. The controller may receive input data from the various sensors, process the input data, and trigger the actuators in response to the processed input data based on instruction or code programmed therein corresponding to one or more routines. An example control routine is described herein with regard to FIG. 3.

The control system 214 (e.g., control sub-system) may be configured to monitor a change in a temperature of the fuel vapor canister via sensors coupled to the fuel vapor canister and adjust operation of the fuel tank isolation valve based on the change in temperature of the fuel vapor canister. Additionally in one example, the control system 214 may be configured to determine the functionality of a fuel tank pressure sensor based on the monitored temperature of the fuel vapor canister. Further in one example, the operation of the fuel tank isolation valve may also be adjusted based on an exhaust gas sensor signal such as a signal from the exhaust gas sensor 237.

FIG. 3 shows an example method 300 for controlling a locking mechanism on a fuel cap for refueling a fuel tank in a vehicle. In particular, a fuel cap may be maintained locked or in a closed position until a refueling request is generated and the fuel tank is sufficiently depressurized before refueling. In order to determine when the fuel cap may be unlocked or opened, pressure in the fuel tank may be monitored to determine when a pressure or vacuum in the fuel tank reaches a sufficiently low level so that the fuel cap may be opened for refueling. At 302, method 300 may include determining if the vehicle is operating in an electric mode. For example, the vehicle may be a plug-in hybrid electric vehicle which may be operated in an electric mode with the engine-off. If the vehicle is not operating in electric mode at 302, method 300 proceeds to 306 described below. However, if the vehicle is operating in electric mode at 302, method 300 proceeds to 304. At 304, method 300 includes ceasing purging of fuel vapors from the fuel tank into an internal combustion engine when the vehicle is operating in an electric mode. For example, a fuel vapor purge valve 261 may be closed or maintained closed so that fuel vapors from the fuel tank are not delivered to the engine. Further, while operating in electric mode, the fuel tank may be sealed off from a fuel vapor canister and the atmosphere so that diurnal fuel vapors are contained in the fuel tank. In the case of plug in hybrid vehicles, the internal combustion engine may not operate for a prolonged period of time. In such systems, the fuel tank may be sealed and at a relatively high pressure.

At 306, method 300 includes determining if entry conditions are met. Entry conditions may include engine off conditions when an engine of the vehicle is not in operation. For example, the vehicle may be a hybrid electric vehicle operating in an engine off mode and being powered by batteries in the vehicle. As another example, entry conditions may include a key-off event wherein the vehicle is turned off, e.g., where the vehicle is parked or is not in use and the engine is not running. Entry conditions may be further based on temperatures in the fuel system or evaporative emission control system, e.g., entry conditions during engine-off conditions may be based on a temperature in the fuel system less than a threshold temperature or greater than a threshold temperature. For example, entry conditions may include determining if a temperature in the fuel system is in a predetermined range of temperatures.

If entry conditions are met at 306, method 300 proceeds to 308. At 308, method 300 includes determining if a refuel request occurs. For example, a refuel request may comprise a vehicle operator depression of a button, e.g., refueling button 197, on a vehicle instrument panel in the vehicle, e.g., instrument panel 196. Thus, the refuel request may include manually requesting opening of a fuel cap coupled to the fuel tank. For example, a vehicle operator may provide input to the vehicle system indicating a desire to refuel the vehicle. If a refuel request occurs at 308, method 300 proceeds to 310.

At 310, method 300 includes venting the fuel tank. For example, the fuel tank may be vented into a vapor absorbent canister, e.g., canister 222, in response to a request to refuel so that the pressure or vacuum in the fuel tank is decreased to a predetermined level in preparation for refueling. For example, the fuel tank may be vented into the vapor absorbent canister through an isolation valve, e.g., isolation valve 253 may be opened.

At 312, method 300 may include determining if a pressure sensor is degraded. For example, a pressure sensor in the fuel system or in the fuel tank, e.g., sensor 291, may be used to monitor pressure in the fuel tank to determine when the fuel tank is sufficiently depressurized for refueling. However, if a fault in the pressure sensor is identified, then pressure changes in the fuel tank may not be able to be determined by the pressure sensor. Determining is the pressure sensor is degraded may be based on a variety of sensor diagnostic routines, e.g., performed prior to the refueling request. If the pressure sensor is degraded at 312, method 300 proceeds to 314.

At 314, method 300 includes determining if a predetermined temperature change in the fuel vapor canister occurs. The predetermined temperature change in the fuel vapor canister may indicate a stabilization in temperature of the vapor absorbent canister. For example, the predetermined temperature change in the canister may comprise an inflection in temperature of the canister. For example, an inflection in temperature of the canister may be determined based on a rate of change of temperature in the canister switching from increasing to decreasing. As another example, the predetermined temperature change may comprise a temperature increase in the canister greater than a threshold temperature increase when the fuel tank is pressurized, e.g., with a pressure greater than atmospheric pressure. As another example, if the fuel tank is under vacuum with a pressure less than atmospheric pressure, then the predetermined temperature change may comprise a temperature decrease in the canister greater than a threshold temperature decrease. These temperature changes in fuel vapor canister may be monitored via a temperature sensor in the canister, e.g., temperature sensor 243.

If a predetermined temperature change in the fuel vapor canister does not occur at 314, method 300 returns to 310 to continue venting the fuel tank until the fuel tank is sufficiently depressurized. However, if a predetermined temperature change in the fuel vapor canister occurs at 314, method 300 proceeds to 318 to unlock or open the fuel cap. For example, if a fault is identified in a pressure sensor in the fuel system, unlocking the fuel cap may be responsive to the fault so that unlocking occurs based only on a temperature change in the canister when the pressure sensor has failed. The predetermined temperature change in the canister may indicate that pressure in the fuel tank is at a desired level so that the fuel cap may be unlocked or opened so that refueling may be performed.

Returning to 312, if the pressure sensor is not degraded at 312, then the method proceeds to 316. At 316, method 300 includes determining if a predetermined temperature change in the fuel vapor canister occurs and/or if a predetermined pressure reading from the pressure sensor occurs. In some examples, determining pressure in the fuel tank may be based on readings from a pressure sensor in the fuel system or in the fuel tank, e.g., pressure sensor 291, and readings from a temperature sensor in the fuel vapor canister, e.g., temperature sensor 243. For example, sufficient depressurization of the fuel tank may be indicated based on both a pressure reading in the fuel system and based on a predetermined temperature change in the canister as described above.

If the conditions of step 316 are not met, then method 300 returns to 310 to continue venting the fuel tank. However, if the conditions of step 316 are met, then method 300 proceeds to 318 to unlock or open the fuel cap. For example, unlocking the fuel cap may be performed when both a pressure sensor and a temperature change in the fuel vapor canister indicate pressure in the fuel tank is at a desired level.

At 320, method 300 includes determining if the refueling event is complete. If the refueling event is not complete at 320, then method 300 proceeds to 322 to maintain the fuel cap unlocked and the fuel tank vented until the refueling event is complete. Once the refueling event is complete at 320, method 300 proceeds to 324. At 324, method 300 includes locking or closing the fuel cap, and at 326, method 300 includes discontinuing venting the fuel tank. For example, after refueling is complete the fuel cap may be closed and locked and the fuel tank isolation valve 253 may be closed to seal the fuel tank from the canister and atmosphere.

FIG. 4 illustrates an example method, e.g., method 300 described above, for unlocking a fuel cap after the fuel tank is sufficiently depressurized. The graph 402 in FIG. 4 shows actuation of a refueling button, e.g., refueling button 197, versus time. The graph at 404 shows actuation of a fuel tank isolation valve (FTIV), e.g., valve 353, versus time. The graph 404 shows actuation of a fuel cap or fuel door or fuel cap locking mechanism, e.g., locking mechanism 245, versus time. The graph 408 shows canister temperature, e.g., as measured by temperature sensor 243, as a function of time. The graph 410 shows fuel tank pressure, e.g., as measured by pressure sensor 291, versus time.

At time T1 in FIG. 4 a refueling request is generated as indicated by actuation of the refueling button. In response to the refueling request, the isolation valve is actuated to an open position to vent the fuel tank to the fuel vapor canister and the atmosphere so that pressure in the fuel tank is decreased in preparation for refueling. As shown in graph 410, after the fuel tank is vented to the canister, pressure in the fuel tank begins to decrease as fuel vapor is vented from the fuel tank into the canister. As fuel vapor from the fuel tank is adsorbed in the canister, the temperature in the canister begins to increase, as shown in graph 410. At time T2, a predetermined temperature change 416 occurs in the canister indicating that the fuel tank is sufficiently depressurized. For example, the predetermined temperature change may be an inflection point in the temperature change of the canister or may be an amount of temperature change in the canister greater than a temperature threshold 412, e.g., a temperature increase to the threshold 412. Further, as shown in graph 414, the pressure in the fuel tank decreases to a pressure threshold 414 indicating that the fuel tank is sufficiently depressurized for refueling. Thus, at time T2, the fuel door or cap may be actuated or unlocked, as indicated in graph 406, so that refueling may be performed.

FIG. 5 shows a method 500 for operating an engine system. The method 500 may be implemented via one or more of the engine systems described above with regard to FIGS. 1 and 2 or may be implemented via other suitable engine systems, in other examples. Specifically in one example, the control sub-systems described above with regard to FIGS. 1 and 2 may be used to implement the steps in method 500. Additionally, the method of FIGS. 5-6 may be performed in a vehicle system in combination with the methods of FIG. 3.

At 501 the method includes routing fuel vapors from a fuel tank into a fuel vapor canister. However, in other examples fuel vapors may not be routed to the fuel vapor canister. At 502 the method includes determining if a fuel tank pressure sensor is degraded. Determining fuel tank pressure sensor degradation may include determining that a fuel tank pressure sensor has been set. Additionally or alternatively, fuel tank pressure sensor degradation may be determined by comparing a signal from the fuel tank pressure sensor to an expected profile of the fuel tank pressure sensor. If it is determined that the fuel tank pressure is not degraded (NO at 502) the method returns to 502 or alternatively ends. However, if it is determined that the fuel tank pressure sensor is degraded (YES at 502) the method advances to 504.

Next at 504 the method includes monitoring a change in a temperature of a fuel vapor canister coupled to a fuel tank via a canister temperature sensor. Monitoring the change in temperature of the fuel vapor canister may include receiving and/or processing a signal from a canister temperature sensor. In one example, the canister temperature sensor may include one or more thermocouples. However, other types of temperature sensors have been contemplated.

At 506 the method includes determining a fuel tank pressure based on the change in temperature of the fuel vapor canister. In one example, the fuel vapor canister temperature can be correlated to the fuel tank pressure. In such an example, this correlation may be predetermined prior to vehicle manufacture and stored in a lookup table in memory of a control system. However in other examples, alternate or additional techniques may be used to associate the fuel vapor canister temperature to the fuel tank pressure. For instance, the response rate of the canister temperature sensor may be used to determine the fuel tank pressure. Still further in other embodiments, the temperature of the fuel vapor canister may be used in conjunction with other inputs such as engine speed, ambient temperature, throttle position, fuel injection rate, etc.

Next at 508 the method includes adjusting operation of a fuel tank isolation valve based on the change in temperature of the fuel vapor canister. Specifically, in one example, operation of the fuel tank isolation valve may be adjusted based on the fuel tank pressure determined at step 506. In this way, a second sensor can be used to infer tank pressure which can be used for subsequent venting operation, thereby decreasing the likelihood of undesirable venting operation due to sensor failure. Consequently, venting operation reliability can be improved.

Adjusting operation of the fuel tank isolation valve may include steps 510-512. At 510 the method includes activating the fuel tank isolation valve to control tank pressure. It will be appreciated that activating the fuel tank isolation valve may include sending a signal to the valve and determining if the valve responds to the signal. At 512 the method includes closing the fuel tank isolation valve when an increase in the temperature of the fuel vapor canister is discontinued. Thus, the fuel tank isolation valve can be closed when the temperature of the canister plateaus. In one specific example, it may be determined that the temperature has plateaued when a rate of change in the temperature is less than a threshold value. In yet another example, operation of the fuel tank isolation valve may also be adjusted based on an exhaust gas sensor signal, to further improve isolation valve operation. Adjusting operation of the fuel tank isolation valve may also include opening the fuel tank isolation valve when the temperature of the fuel vapor canister indicates that the fuel tank is above a threshold pressure.

At 514 the method includes purging the fuel vapor canister into an intake system while the fuel tank isolation valve is closed. In this way, purging operation can be implemented to reduce evaporative emissions. It should be appreciated that when the answer to 502 is no, the routine continues to monitor for pressure sensor degradation without performing any of the actions of blocks 504, 506, 508, 510, 512, and/or 514. For example, the fuel tank isolation valve operation is not adjusted based on the temperature change when the answer to 502 is no, but rather based on other parameters as desired or as described above herein.

FIG. 6 shows a method 600 for operating an engine system. The method 600 may be implemented via one or more of the engine systems described above with regard to FIGS. 1 and 2 or may be implemented via other suitable engine systems, in other examples. Specifically in one example, the control sub-systems described above with regard to FIGS. 1 and 2 may be used to implement the steps in method 600.

At 602 the method includes infer a fuel tank pressure based on one or more of an ambient temperature, an engine temperature, a fuel tank level, and an air flow. It will be appreciated that the air flow may be the flowrate of intake air through an intake system. In this way, fuel tank pressure can be inferred from a variety of variables when a fuel tank pressure sensor is degraded, for example. Thus in one example, step 602 may be implemented subsequent to determining that a fuel tank pressure sensor is degraded. In other examples, additional or alternative variables may be used to determine fuel tank pressure. Further in one example, the method may include routing fuel vapors from the fuel tank to the fuel vapor canister prior to step 602.

At 604 the method includes determining if the inferred fuel tank pressure is greater than a threshold value. In one example, the threshold value may be predetermined. If it is determined that the inferred fuel tank pressure is not greater than the threshold value (NO at 604) the method returns to 604. However, if it is determined that the inferred fuel tank pressure is greater than the threshold value (YES at 604) the method advances to 606. At 606 the method includes opening a fuel tank isolation valve. As previously discussed, the fuel tank isolation valve is coupled between the fuel tank and the fuel vapor canister. Thus, the fuel tank isolation valve is configured to meter the amount of fuel vapors flowing between the fuel tank and the fuel vapor canister. In this way, fuel vapor can be flowed to the vapor canister, to decrease pressure in the fuel tank.

Next at 608 the method includes monitoring a change in a temperature of the fuel vapor canister coupled to a fuel tank via a canister temperature sensor. Monitoring the change in temperature of the fuel vapor canister may include receiving and/or processing a signal from a temperature sensor coupled to the fuel vapor canister.

At 610 the method includes determining if the fuel vapor canister temperature has stabilized. Specifically in one example, it may be determined if the fuel vapor canister temperature has plateaued. Exemplary techniques for determining a temperature plateau are discussed above with regard to method 500.

If it is determined that the fuel vapor canister temperature has not stabilized (NO at 610) the method returns to 610. However, if it is determined that the fuel vapor canister temperature has stabilized (YES at 610) the method advances to 612. At 612 the method includes closing the fuel tank isolation valve. In this way, the fuel tank isolation valve may be adjusted based on the change in temperature of the fuel vapor canister. It will be appreciated that the fuel vapor canister may be purged while the fuel tank isolation valve is closed, in one example.

FIG. 7 shows a method 700 for operating an engine system. The method 700 may be implemented via one or more of the engine systems described above with regard to FIGS. 1 and 2 or may be implemented via other suitable engine systems, in other examples. Specifically in one example, the control sub-systems described above with regard to FIGS. 1 and 2 may be used to implement the steps in method 700.

At 702 the method includes monitoring a change in a temperature of the fuel vapor canister coupled to a fuel tank via a canister temperature sensor. As previously discussed, monitoring a change in temperature may include receiving and/or processing a temperature sensor signal.

Next at 704 the method determines if the fuel tank pressure sensor is functioning. It will be appreciated that the functionality of the fuel tank pressure sensor may be based on the monitored change in temperature of the fuel canister. Specifically in one example, an expected fuel vapor canister temperature profile may be compared to the monitored fuel vapor canister temperature profile to determine fuel tank pressure sensor functionality.

If it is determined that the fuel tank pressure sensor is functioning (YES at 704) the method advances to 706. At 706 the method includes adjusting operation of the fuel tank isolation valve based on the fuel tank pressure sensor.

However, if it is determined that the fuel tank pressure sensor is not functioning (NO at 704) the method advances to 708. At 708 the method includes indicating fuel tank pressure sensor degradation. In one example, indicating fuel tank pressure sensor degradation may include setting a flag in the control system, triggering a pressure sensor degradation indicator, etc.

Next at 710 the method includes adjusting operation of the fuel tank isolation valve based on the change in temperature of the fuel vapor canister. In this way, fuel tank isolation valve operation can be carried out based on a 2^(nd) sensor (i.e., the fuel vapor canister temperature sensor when the fuel tank pressure sensor is degraded, thereby increasing the reliability of isolation valve operation.

FIG. 8 shows a first graph 800 and a second graph 802 depicting the correlation between the fuel vapor canister temperature and the fuel tank pressure. The first graph 800 shows a plot 804 of the fuel vapor canister temperature sensor, the second graph 802 shows a plot 806 of the fuel tank pressure. A third graph 803 shows a plot 808 of a duty cycle of the fuel tank isolation valve. As shown, the plots 804 and 806 have an inverse correlation.

Note that the example control and estimation routines included herein can be used with various engine and/or vehicle system configurations. The control methods and routines disclosed herein may be stored as executable instructions in non-transitory memory and may be carried out by the control system including the controller in combination with the various sensors, actuators, and other engine hardware. The specific routines described herein may represent one or more of any number of processing strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, various actions, operations, and/or functions illustrated may be performed in the sequence illustrated, in parallel, or in some cases omitted. Likewise, the order of processing is not necessarily required to achieve the features and advantages of the example embodiments described herein, but is provided for ease of illustration and description. One or more of the illustrated actions, operations and/or functions may be repeatedly performed depending on the particular strategy being used. Further, the described actions, operations and/or functions may graphically represent code to be programmed into non-transitory memory of the computer readable storage medium in the engine control system, where the described actions are carried out by executing the instructions in a system including the various engine hardware components in combination with the electronic controller.

In another representation a method comprises, via an electronic controller in combination with an engine and fuel system, routing fuel vapors from a fuel tank into a fuel vapor canister; and when (or in response to) a fuel tank pressure sensor is degraded, monitoring a change in a temperature of the fuel vapor canister to determine if pressure in the fuel tank is below a threshold. The temperature change may be monitored via a temperature sensor coupled in the fuel vapor canister measuring an internal temperature of the canister. The fuel tank pressure sensor degradation may be determined in various ways, such as based on whether the fuel tank pressure changes agree with fuel tank temperature changes of a fuel tank temperature sensor. In response to the determined fuel tank pressure being below the threshold, various actions may be taken including setting a diagnostic code and sending a visual message to a vehicle operator.

In another representation, a method comprises routing fuel vapors from a fuel tank into a fuel vapor canister; and in response to a fuel tank pressure sensor being determined as degraded via a control system in combination with the engine and fuel system, indicating that pressure in the fuel tank is at a desired level based on a change in a temperature of the fuel vapor canister. Again, various actions may be taken in response to the indication including performing a leak test, adjusting engine operation, and/or adjusting vehicle operation. In still another representation a method comprises, in response to a refuel request, venting a fuel tank into a fuel vapor canister to depressurize the fuel tank; and if a fuel tank pressure sensor is determined to be degraded, unlocking a fuel cap only after a stabilization in a temperature of the fuel vapor canister. In yet another representation, a method comprises when a fuel tank pressure sensor is degraded, inferring fuel tank pressure based on one or more of ambient temperature, engine temperature, fuel level indicator, and air flow; and if inferred fuel tank pressure is greater than a threshold, performing each of opening a tank pressure control valve, monitoring a canister temperature; and closing the tank pressure control valve only after the canister temperature is stabilized, for example it has reached a level that does not change by more than 5% over a threshold duration, such as 1 minute.

It will be appreciated that the configurations and routines disclosed herein are exemplary in nature, and that these specific embodiments are not to be considered in a limiting sense, because numerous variations are possible. For example, the above technology can be applied to V-6, I-4, I-6, V-12, opposed 4, and other engine types. The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations, and other features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations and sub-combinations regarded as novel and non-obvious. These claims may refer to “an” element or “a first” element or the equivalent thereof. Such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and sub-combinations of the disclosed features, functions, elements, and/or properties may be claimed through amendment of the present claims or through presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, also are regarded as included within the subject matter of the present disclosure. 

1. A method for operating a vehicle system comprising: monitoring a change in a temperature of a fuel vapor canister coupled to a fuel tank via a canister temperature sensor; and adjusting operation of a fuel tank isolation valve based on the change in temperature of the fuel vapor canister.
 2. The method of claim 1, further comprising determining a fuel tank pressure based on the change in temperature of the fuel vapor canister.
 3. The method of claim 2, where a response rate of the canister temperature sensor is used to determine fuel tank pressure.
 4. The method of claim 2, where monitoring the change in temperature of the fuel vapor canister and determining the fuel tank pressure are implemented subsequent and in response to determining fuel tank pressure sensor degradation.
 5. The method of claim 2, where operation of the fuel tank isolation valve is adjusted based on the determined fuel tank pressure.
 6. The method of claim 1, where adjusting operation of the fuel tank isolation valve includes closing the fuel tank isolation valve, the method further comprising purging the fuel vapor canister into an intake system while the fuel tank isolation valve is closed.
 7. The method of claim 1, further comprising determining the functionality of a fuel tank pressure sensor based on the monitored temperature of the fuel vapor canister.
 8. The method of claim 1, where adjusting operation of the fuel tank isolation valve includes closing the fuel tank isolation valve when an increase in the temperature of the fuel vapor canister is discontinued.
 9. The method of claim 1, further comprising prior to monitoring the change in temperature of the fuel vapor canister and when a fuel tank pressure sensor is degraded, inferring a fuel tank pressure based on one or more of an ambient temperature, an engine temperature, a fuel tank level, and an air flow.
 10. The method of claim 9, further comprising if the inferred temperature is greater than a threshold value, adjusting operation of a fuel tank isolation valve includes opening the fuel tank isolation valve.
 11. A vehicle system comprising: a fuel vapor canister coupled to a fuel tank; a canister temperature sensor coupled to the fuel vapor canister; a fuel tank isolation valve coupled between the fuel vapor canister and the fuel tank; and a control sub-system configured to: monitor a change in a temperature of the fuel vapor canister via sensors coupled to the fuel vapor canister; and adjust operation of the fuel tank isolation valve based on the change in temperature of the fuel vapor canister.
 12. The vehicle system of claim 11, where the control sub-system is further configured to determine the functionality of a fuel tank pressure sensor based on the monitored temperature of the fuel vapor canister.
 13. The vehicle system of claim 11, where the operation of the fuel tank isolation valve is also adjusted based on an exhaust gas sensor signal.
 14. The vehicle system of claim 11, where the system is included in a hybrid electric vehicle.
 15. The vehicle system of claim 11, where the canister temperature sensor includes one or more thermocouples.
 16. A method, comprising: routing fuel vapors from a fuel tank into a fuel vapor canister; when a fuel tank pressure sensor is degraded, determining a fuel tank pressure based on a monitored change in temperature of the fuel vapor canister; and adjusting a fuel tank isolation valve based on the determined fuel tank pressure.
 17. The method of claim 16, where the operation of the fuel tank isolation valve is also adjusted based on an exhaust gas sensor signal.
 18. The method of claim 16, further comprising indicating that the fuel tank pressure is above a threshold pressure when it is determined that the change in temperature is above a threshold value.
 19. The method of claim 16, where adjusting operation of the fuel tank isolation valve includes closing the fuel tank isolation valve when an increase of the temperature of the fuel vapor canister is discontinued.
 20. The method of claim 16, where a response rate of the canister temperature sensor is used to determine fuel tank pressure. 